The present invention relates to a suspension trailing arm, and in particular to a composite suspension trailing arm for a heavy commercial vehicle.
Heavy commercial vehicles typically employ trailing arm suspension systems, particularly in relation to the rear axles of rigid body vehicles or the axles of trailers of articulated vehicles.
Heavy commercial vehicles (including trucks, buses and coaches) can be distinguished from light commercial vehicles (such as vans) and light passenger vehicles due to one or more of the following characteristics: 1) a laden weight in excess of approximately 3.5 tons, and 2) the use air actuated brakes as opposed to hydraulically actuated brakes (because air actuated brakes are better able to withstand the increased heat generated by the repeated braking of a vehicle having a weight greater than approximately 3.5 tons).
Such vehicles (including trailers) also typically employ a pair of spaced parallel beams that extend the length of the vehicle and act as a chassis upon which the vehicle body is mounted.
When used in heavy commercial vehicles, the front of the trailing arms are typically pivotally mounted to the chassis beams of the vehicle. Each of the trailing arms extend rearwardly (i.e., towards the rear of the vehicle) to a mounting position for the axle and then further rearwardly to a mounting surface for an air spring that is mounted between the trailing arm and the vehicle chassis. Axles in these vehicles are typically substantially rigid beam-type axles. In some circumstances, the orientation of the trailing arms may be reversed to pivot at the rear of each of the trailing arms, in which case they are known as “leading arms.” For the purposes of this specification, the term trailing arm should also be understood to encompass leading arms.
Known heavy vehicle trailing arms are typically constructed either from solid spring steel trailing arms provided with U-bolts and plates that connect the axle to the trailing arm, fabricated steel plate which is then welded to an axle or axle adapter, or a hybrid of these two types of trailing arms. One such fabricated trailing arm is disclosed in U.S. Pat. No. 5,639,110 issued to Pierce et al.
Both prior art types of trailing arms provide a rigid connection between the trailing arm and the axle to resist bending, but have a resilient connection between the chassis and the axle. The resilient connection is provided either by the flexing of the spring steel trailing arm or by the flexing of a large elastomeric bushing (resilient bearing) located in the end of the fabricated trailing arm between the chassis and the trailing arm. This enables articulation forces induced during vehicle use to be taken up, while maintaining tracking and roll stability. For fabricated trailing arms for use in heavy commercial vehicles, it has typically been necessary for the traveling arms to be manufactured having a closed box-section profile to impart sufficient tracking stability to the trailing arm.
One disadvantage of known manufacturing techniques is that the shape of the trailing arm is restricted, which in turn restricts the positioning of additional components that are mounted to the trailing arms, such as brakes, air springs, dampers and pivot bushings. This may cause the suspension packaging (i.e., its space requirement) to be inefficient. Another disadvantage of known trailing arms is that it is timely to secure the trailing arm to the axle, for example, by fastening or welding.
The desire to reduce the weight of vehicle components means it also desirable to provide a trailing arm of reduced weight which provides comparable flexibility to known spring steel trailing arms.